Various conditions of the spine, such as herniated discs, arthritis (spondylosis), misalignment of the spine (spondylolisthesis, scoliosis or hyperlordosis/kyphosis) can be treated with minimally invasive surgery, which is accomplished through narrow channels created and maintained by expandable bladed retractors. For example, Lumbar Interbody Fusion surgery is used to fuse adjacent vertebra, to treat a variety of conditions. The surgery entails removal of a portion of an intervertebral disc, placement of a “cage” or “interbody fusion device” between the discs, and placement of bone graft material between the discs (and subsequent installation of screws and posts to hold the two vertebrae in place while they fuse together). To gain access to the intervertebral disc in a minimally invasive surgery, a surgeon may approach the spine through a retractor system placed in one of several pathways. The spine may be approached from the side of the patient (lateral lumbar interbody fusion), from the front of the patient (anterior lumbar interbody fusion), obliquely from the front of patient (oblique lumbar interbody fusion), from the back of the patient (posterior or transforamen lumbar interbody fusion), and obliquely from the back of the patient (oblique lateral interbody fusion). Especially for the deeper routes (anterior, oblique, and lateral routes), a retractor system with long retractor blades is used, and visualization is currently obtained through a surgical loop or a surgical microscope intermittently looking down the passage. These instruments are necessarily disposed quite a distance from the surgical opening, making it difficult to view the surgical space, and require a surgeon to look through the loop or microscope, which may require taking on an uncomfortable posture while performing surgery. Visualization through an endoscope has also been proposed, with the endoscope disposed within the channel established by the retractor blades and extending to the distal end of the blades, near the surgical field. The endoscope takes up valuable space within the channel, and does not provide a view of tool tips within the channel, and the field of view may be limited if the endoscope is placed close to the surgical field.